The semiconductor device fabrication process uses various cleaning methods of cleaning a semiconductor wafer (to be referred to as “a wafer” hereinafter). A known example is a method of processing a wafer by immersing it in a processing bath containing a chemical solution such as dilute hydrofluoric acid (DHF), rinsing the processed wafer by immersing it in a processing bath containing purified water, immersing the rinsed wafer in a processing bath containing isopropyl alcohol (IPA), and drying the wafer by using the marangoni effect by slowly pulling up the wafer from this processing bath or discharging IPA from the processing bath (e.g., Patent Documents 1 and 2).
Recently, however, the micropatterning of a circuit pattern formed on a wafer is advancing, and the strength of a projection of the pattern has decreased. If a wafer having a circuit pattern like this formed on it is processed by the above processing method, therefore, the formed pattern (projection) falls in the drying process.
This pattern fall presumably occurs because if the projection of the circuit pattern exists in the boundary between a gas phase and liquid phase when the wafer is pulled up from the IPA processing bath (or when IPA is drained from the IPA processing bath), the magnitude of a force acting on the projection loses its balance due to the surface tension of IPA between the gas phase side and liquid phase side of the projection.
Another known example of the wafer cleaning method is to process a wafer by immersing it in a processing bath containing a chemical solution such as dilute hydrofluoric acid (DHF), rinse the processed wafer by immersing it in a processing bath containing purified water, and dry the rinsed wafer pulled up from the processing bath by supplying vapor of isopropyl alcohol (IPA) to the wafer.
In this substrate drying method, the wafer temperature rises when the IPA vapor condenses on the surface of the wafer, and IPA sticking to the wafer volatizes after that due to this temperature rise. In this case, a watermark is formed by the evaporation of purified water if there is a portion where purified water sticking to the wafer is not well replaced with IPA.
A known processing method that suppresses the formation of this watermark is to use an apparatus capable of storing purified water in a water bath, forming a layer of water vapor within a predetermined range above the water surface, and also forming a layer of IPA vapor above the water vapor layer, and pull up a wafer immersed in the purified water toward the IPA vapor layer (e.g., Patent Document 3).
Unfortunately, the strength of projections forming circuit patterns has decreased with the recent progress of micropatterning of circuit patterns. When a wafer is processed by this processing method, therefore, in a projection positioned near the boundary between the water vapor layer and IPA vapor layer, drying by the IPA vapor has started in the upper portion of the projection, whereas the water film formed by the water vapor remains in the lower portion of the projection. This makes the magnitude of the surface tension acting on this projection on the side above the boundary between the water vapor layer and IPA vapor layer different from that on the side below the boundary. As a consequence, the projection may fall.    Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 63-23326    Patent Document 2: Jpn. Pat. Appln. KOKAI Publication No. 2003-243351    Patent Document 3: Jpn. Pat. Appln. KOKAI Publication No. 11-176798